The use of nickel-zirconia cermet anodes for solid oxide electrolyte fuel cells is well known in the art, and taught, for example, by A. O. Isenberg in U.S. Pat. No. 4,490,444. This fuel electrode or anode must be compatible in chemical, electrical, and physical-mechanical characteristics such as thermal expansion, to the solid oxide electrolyte to which it is attached. A. O. Isenberg in U.S. Pat. No. 4,597,170 solved bonding and thermal expansion properties between the anode and solid oxide electrolyte, by use of a skeletal embedding growth, of for example, primarily ionic conducting zirconia doped with minor amounts of yttria, covering lower portions a porous nickel powder layer comprising the porous cermet anode.
This anchoring of the anode nickel particles to the solid oxide electrolyte was accomplished by a modified chemical vapor deposition process, usually providing a dense deposit. While this process provided well bonded anodes, having good mechanical strength and thermal expansion compatibility, gas diffusion overvoltages were observed during operation, lowering overall cell performance. Additionally, these anodes were not found to be particularly tolerant of sulfur contaminants.
In order to reduce gas diffusion overvoltages A. O. Isenberg et al., in U.S. Pat. No. 4,582,766, taught oxidizing the nickel particles in the cermet electrode to form a metal oxide layer between the metal particles and the electrolyte, while additionally providing porosity in the embedding skeletal member, and then reducing the metal oxide layer to form a porous metal layer between the metal electrode particles and the electrolyte; all allowing greater electrochemical activity. Such structures were still not found to be particularly sulfur tolerant, however, and provide a limited number of electrochemical sites. What is needed is a sulfur tolerant anode structure having low diffusion overvoltages coupled with long periods of acceptable performance.